Composition of metamorphic rocks and some aspects of evolution of the Lapland Granulite Belt on the Kola Peninsula, USSR

Composition of metamorphic rocks and some aspects of evolution of the Lapland Granulite Belt on the Kola Peninsula, USSR

NIKOLAI E.KOZLOV& ANDREIA.IVANOV

Kozlov,N.E.&Ivanov,AA 1991:Composition ofmetamorphic rocks and some aspectsof evolution of theLapland Granulite Belt onthe KolaPeninsula,USSR.Nor.geol.unders.Bull.421,19-32.

Combined geologicaland petrochemical datasuggest thattheLaplandGranuliteBeltcan bedivi- ded into alower sedimentary-volcanic unit andanupper,predominantly sedimentary sequence.

Metamorphicrocksfromthe lower partsof the section have givenzircon agesof2.7- 2.8Ga.

The geochemical signatures ofthemetavolcanites andmetased imentary rocks suggest that the Lapland granulites arecomparableto Phanerozoic island arc complexes.The compositionof the pre-Lop ian basement blocks is in agreement with this hypothesis. According to ourproposed model,thedevelopment of theBeltwasinitiated by underthrusting oftheBelomorian blockben- eaththe Kolablock.Thisledtowidespreadvolcanic activity,whichwaseventually superseded by the sedimentary cycle.The complexwas thentakendown todepths sufficient for metamorphic transformations ingranulitetacies:thisoccurred ataround1.9- 2.0Ga.

Nikolai E.Kozlo v,Andrei A. Ivanov,Geological Institute,Kola ScienceCentre, USSR Academy of Sciences,Apatity 184200,USSR.

Introduction

Data obtained from various regions .of the world indicate that a considerable proportion of granulite terrains occur in the most ancient formations of mobile belts. This explains why a study of these terrains is of great importan- ce for the investigation of the early stages of evolution of the Earth's crust and its metal- logenic properties. Examination of the primary nature and pre-metamorphic structure of strongly metamorphosed Archaean sequences presents diff iculties since the shapes of geolo- gical bodies, and structures and textures of the rocks differ from those in the initial state , and it is also difficult to decide whether the primary form of rock layers has been preser- ved. Petrochemical study of supracrustal for- mations, however, provides an efficient means of reconstructing the conditions of sedimenta- tion and volcanism.

The present work is the result of long-term investigations (1977 - 1990) carried out by the authors in the Lapland Granulite Belt in the territory of the USSR. It should be cons idered in conjunction with the investigations started by Mikkola (1941), Eskola (1952), Belyaev (1971) and Mer ilalnen (1976), and continued later by Vinogradov et al. (1980), Barbey et al. (1980, 1984, 1986), Horrnann et al. (1980),

Krylova (1983), Marker (1985) and Raith

Raase (1986).

The results of our investigations are based on geological and geochemical data compr i- sing over 600 complete silicate chemical analy- ses (more than a half of them are original) and about 400 quant itative determ inations of minor element contents , conducted at the Geological Institute of the Kola Science Cen- tre of the USSR Academy of Sciences, in Apatity. The limited length of the paper does not allow us to document the results in full;

consequently, in some cases, we outline only the most significant conclusions and emphas i- ze the results of the geochemical studies.

Regional setting

Integrated geolog ical and geophys ical investi-

gations of the Granulite Belt enabled us earl-

ier (Kozlov 1983, 1988a) to suggest that it

consists of two parts: a lower sedimentary-

volcanic unit and an upper, originally sedimen-

tary sequence (Fig. 1). It should be noted that,

like many geologists (Belyaev 1971, Krylova

1983), we believe that the Belt is composed

of both the granu lite rock complex and the

rocks occur ring in the south-southwest adja-

cent to the yranulites and metamorphosed

20 NikolaiE. Kosto v&AndreiA.Ivano v

-

SOVIET UNIO

-:~

G 0

!

b"

~ 6"

JO'

,,," \ ^, _,

Fig.1.Simplifiedgeolog icalmap ofthet.aptanoGranulite Belt: based on Barbey et al. (1980). Mark er (1985) and Predovs y(1987).Arabic numeralsindicate thelocationof metavolcanitesfromthelower(1)sequence ofthe beltand metasedimentaryrocks from theupper(2) sequence.3.4 -EarlyArcnaeanmetamorphicsequencesofthe Belomori- anandKolamegablocks,respectively.AB- lineofsection, Salnytundra;C-H - terrains:C-Korvatundra;D-Kolvit- satundra;E-Allarechensk;F - Kolmozer o -Voronya;G - trnandra:H- Terskyblock.

Thedetailed map(below)showsthe geology ofthe north- western part of the laplandGranulite Belt(Kozlov et al.

1990).legend:Supracrustalandultrametamorphicformati- ons:1-garnet amphibolitesand meso-melanocratic pyroxe- ne-plagioclase scnists, commonly with garnetandlocally withbiotiteand amphibole;2-gneisses andamphibolites of theperipheralareas:3-garnet-biotitegneisses,granitic gnelsses,quartz-feldspar granuliteswithgarnetandsillima- nite-biotite-garnet-quartz -feldspargranulites ;4-endebites.

Intrusions:5 -plagiomicroc line granites; 6- diorites:7 -

metagabbro-anorthosites. Other symbols: 8 - geological boundaries(a-defined,b- hypothetical):9 -tectonicboun- daries and major fracturezones;10- foliation.

under amphibolite-facies conditions. The latter rock comp lex is distinguished by many investi- gators of the Norwegian and Finnish frag- ments of the Granulite Belt as the Tanaelv Belt (Barbey et al. 1984, 1986; Marker 1985),

Our opinions are presented in the mono- graph of Kozlov et al. (199Gb), and here we list only the major groun ds for this interpreta- tion:

GU-BULL.J2 1.199 1

1. According to the available data there is no break in sedimentat ion in the sequences of the above-mentioned complexes . Lateral- ly within the Belt the boundary of granulite metamorp hism occupies different positions in the section relative to the primary varie- ties of metamorphosed volcanic rock s that subsequently replace each other in the Belt. This has been described, for examp- le, from the Salny tundra area (Kozlov et al. 1 988a); see Fig. 2.

2. Metamorphosed volcanic rock s of both complexes have similar geochemical prop- erties. The same has been described by Barbey et al. (1984, 1986) for the rocks occurr ing in Finland. A special emphasis should be given to the fact that all rock types, irrespective of their met amorphic grade, have increased cont ents of stront ium and, in some cases, barium. This we relate to a particular regime of form ation of the sequences in the who le complex at the pre-metamorph ic stage (Kozlov et al. 1989), Considering this approach to the interpretation of the overall structure , we believe that it inclu- des the Korva tundra rocks located in the southwestern part of the Belt, in the USSR, where conglomerates with pebbles of plagio- clase granite, similar to those desc ribed for the Kolvitsa tundra area, are nown near the basal contact. The novelty of this interpretation is that one of the authors (A.A.I.) co nsiders the main Korva tundra structure to be an anti- cline (Fig. 3), This assumpt ion is supported by the data on the chemical com position of the rocks from the zone near to the contact (Table 1). The contact structure is analogous to that report ed from the Salny and Kolvitsa tundras (Kozlov et al. 199Gb). Accepting that our suggest ions and interpretations are cor- rect, the term 'granulite belt' becomes a con- ventional one and does not reflect the nature of the metamorph ism in the structure as a who le; hereafter it is used only because of tradition.

Up to the prese nt there are no reliable radio-

metr ic datings which allow one to speak about

an Arch aean age for the Belt. The age of 2.6

Ga for the granulites, obtained by Sukhanov

et al. (1987) for metamorphosed volcanites

of the Kolvitsa tundra by the Pb"'- - Pb"'" zir-

con method of therm ionic emission, may be

cons idered only as a preliminary date. As for

the datings of Zykov et al. (1984) yielding 2.78

Ga (Pb-Pb whole-rock age for metamor phosed

NGU - BULL.421,1991 Lapland GranuliteBelt,KolaPeninsula,USSR 21

[ZJ

Q

_~

~4 ~ 5

PJlo ° b ~~7 1 - - 1 8

^{[, /~ 1 ,0}

Fig.2.Schematic cross-section ofthe granulitecomplex ofthe Salny tundra area (A-S inFig.1).Legend: 1-the basement rocks (biotite gneisses);2 - anoesl te-dacttes and dacites (amphibole-biotitegneisses ,locally withpyroxene);3 - tholeiites (garnet amphibolites,pyroxe neschistswith or withoutgarnet): 4 - aluminous basalts(garnet amiphibolites,pyroxeneschists with garnet); 5 - aluminousandesiticbasalts (pyroxene-plagioclase schists withgarnet);6 - greywackes and subgreywac- kes (alkalinegranulites);7 - anorthosi tes; 8 - faults(real andinferred);9-geological boundaries:a - real, b-inferred;10 - mylonitizationzones . I(inset profile) - tentative general interpretationof the section.

volcanltes), they seem to be rather doubtful.

The rocks metamorphosed in granulite facies (andesite tutts) and, in our opinion, constituting the lower parts of the section, were dated to 2.7 Ga (U-Pb zirco n method, Kolvitsa tundra;

Bogdanova

Yefimov 1984). This figure is complemented by the datings of 2.7 - 2.8 Ga obta ined by the lead therm ionic emission method on zircons from metamorp hosed ande- sites of the Kolvitsa tundras (Sukhanov et al.

1987), Korva tundra, and areas to the south - east, which are conside red to belong to one and the same complex (Kozlov et al. 1990a).

These age determinations need to be con- firmed, and this is a subject of our future inves- tigations.

Our suggestion for an Archaean age for the volcanic and sedimentary rocks of the Granu- lite Belt is based on the following:

1. The general nature and characteristic featu- res of the belt - geological structure , as- pects of the chemical composition, and primary features of the rocks - indicate that there is an essential similarity between these formations and the Lopian (Late Ar- chaean) sections of the Kola and Karelian regions that have yielded reliable age deter- minations which are older than Proterozo ic (Predovsky 1987).

2. The rocks of the granulite comp lex lie direct- ly upon formations of the Belomorian (Whi- te Sea) megablock (as shown in Fig. 3) which are considered to be Early Archae- an. The Belomor ian formations , in contrast to the rocks of the Granulite Belt, have been affected by two additional stages of deformation (Balagansky et al. 1986). If the granulites were of Proterozo ic age, then

Table 1.Chemical composition of the rocks from the contact zone of the Granulite Selt andthe basement complex,Korva tundra area.

Sample no. SiO, TiO, AI,O, Fe,O, FeO MnO MgO CaO Na,Q K,Q

2493 66.28 1.29 14.03 5.45 3.25 0.03 0.82 0.95 2.78 3.11

2486 62.37 0.70 19.00 3.50 3.69 0.06 1.62 1.76 2.43 2.03

IA-101l1 49.94 2.84 13.29 6.27 10.00 0.23 4.99 8.86 1.36 0.37

2477 51.06 1.63 11.14 0.41 10.41 0.21 8.68 10.33 2.99 0.41

2479 71.75 0.37 12.82 1.33 1.88 0.02 2.11 1.18 4.49 2.80

IA-108 67.94 0.40 13.30 0.81 3.66 0.02 3.45 1.88 3.91 2.42

2474 71.80 14.42 0.00 2.68 0.02 1.00 0.55 7.90 0.38

2476 64.61 0.68 16.76 2.50 5.79 0.10 2.06 1.24 1.24 2.09

2484 81.23 0.17 11.15 1.09 0.36 0.00 40.27 0.00 0.46 3.25

2483 46.78 0.19 17.55 2.05 3.89 0.11 10.56 14.56 1.60 0.19

2498 52.67 0.25 22.08 2.18 1.07 0.14 2.36 12.73 4.10 0.39

2481 67.52 0.12 15.28 1.30 2.90 0.06 1.15 3.52 4.94 1.97

2495 65.14 ^{0.48 14.98 2.00 2.49 0.03 3.34 2.40 5.25 2.16}

IA-l07 49.73 1.26 14.22 1.63 10.55 0.21 6.87 10.60 2.56 0.45

Note: Samplenumberscorrespondto those inFig.3.

22 NikolaiE.Kosto v&AndreiA.Ivanov ^{NGU-BULL.42 1.199 1}

.::::: 40

• ...J,..

=

v ··

I 'o-

- -

oj _II

5

2 J km

~-,---,-I---11

o

o 2

I

I

1

/ v"vl .. v .. 2

~J

EJ4

Iv ~ 1 5

I ===j ⁶ 1 °0 °17

~ o~

~8 ~ 12

~9 C~ fG

1 # #1 10 1 ~l f4

Fig.3.(a) Schematicgeologicalmap ofthecontact zonebetween the granulite-gneissesandgranulitecomplexesinthe area oftheM.Korva-tundra.(b)Enlargement of thearea framedin(a).(c)- schematic section of the contactzoneinthe areaof the riverPados, notto scale. Legend:Belomoriancomplex: 1-biotitegneisses;2- amphiboJiteswithgarnet. Lopiancomplex:3 -plagioclaseamphiboJites;4 - garnet amphibolites;5 - amphiboJitegneisses;6-biotite-amphibolegneisses;7- metamor- phosedconglomerates;8-muscovite-quartzgneiss-schists;9-gabbroanorthosites;10-paJingeneticgranitoids;11 -Oua- ternary deposits;12 -real(a) andinferred(b) geologicalboundaries;13-(a)observationpoints and(b)-strikeand dipof foliation;14 - plungeof fold axes.

NGU -BULL.421,1991

we must infer that there were only two sta- ges of deformation during the late Archaean.

The opinion favouring a probable Archaean (Lopian) age for the Lapland Granulite Belt is fairly popular among soviet geologists (Krylova 1983, Rundkvist

Mitrofanov 1988). Providing that this conception is true, the younger ages reported by Bernard-Griftiths et al. (1984) pro- bably reflect the subsequent metamorphic transformations of the complex at around 2.0 Ga. These transformations were , in our opin- ion, accompanied by processes of enderbitiza- tion, charnockitization and partial melting.

Nevertheless, some of the primary geochemi- cal properties of the various formations survi- ved these changes (Kozlov et al. 1990c).

Geochemical features of metamorphosed volcanic and sedimentary rocks

Specific features of the primary composition of the supracrustal formations reconstructed by the petrochemical method (Predovsky 1970)

Lapland Granulite Belt,Kola Peninsula,USSR 23

have been discussed by Kozlov (1983, 1988a).

The most typical rock-types within the belt as a whole have a fairly homogeneous chemical composition (Table 2). The probable primary rock-types of the diverse metamorphic assem- blages are indicated in Table 3.

Metamorphic rocks of a tentatively primary volcanogenic origin constitute the lower part of the section, which begins with tholeiites (group 1 in Table 2) composing about 43-45%

of the total volume of volcanites. Andesites , dacites and andesite tuffs, reaching up to 15-18% by volume, are intercalated with the above rocks. Upwards, the tholeiites are repla- ced by aluminous basalts (group 4, Table 2), which make up 33-35 % of the volume of the volcanites . Aluminous andesitic basalts and andesites, at the top of the metavolcanite section, do not occur everywhere; their volume varies considerably from 0 to 15 %. The alter- nation of basalts, andesites and andesitic tufts in the lower part of the section can be ex- plained by the occurrence of faults located

Table 2.Chemical composition of the main rock types in the Kolvitsa tundras (K),northwestern part of the GranuliteBelt(C) and Lake Inari region (I).

No. Region

K C I

2 K

C I

3 K

C I

4 K

C

5 K

C I

6 K

I

7 K

I

8 K

C I

9 K

C I

Number of samples

18 11 2 4 2 1 16 6 1 10 10 4 5 1 3 1 7 8 17 4 7 5 7 2

SiO, 50.50 49.55 51.52 67.79 64,19 61,08 67,84 68,32 67.37 51,52 50,96 52,78 55,05 52.56 60.53 56.97 78.62 76.75 66.03 67.22 65.13 58,57 63,11 65,89

TiO, AI,O, 1.02 14.46 1.09 14.63 1.30 14.00 0,54 14,88 0,67 13,86 0,51 15.10 0,52 12.57 0.51 13.15 0,74 13.37 0,67 16.86 0.56 18.64 0.69 19.59 0.64 17.29 0.60 19.46 0.47 18.41 1.33 18.11 0,38 10,27 0,31 11,87 0,58 14,77 0,60 14,10 0.69 10,75 0,72 18,52 0.67 17,22 0,54 17,30

Fe,O, FeO 2.48 9.96 2.49 10.27 2.89 9.29 1,68 5.19 1,29 4.27 3,71 4.36 1.45 4.06 1.76 3.74 1.31 2.85 1.89 6,75 1.56 6.04 2.19 4.82 1.59 6,36 1.56 6,80 1.45 3,71 2.06 5,01 0,52 3,30 0,76 2,38 1,31 5,08 1,74 5,61 1,25 4,34 2.10 7.05 1,27 6.59 1,36 4.75

MnO 0,18 0,22 0,23 0,07 0.08 0.14 0.08 0.06 0.08 0.15 0.12 0.11 0.10 0.22 0,07 0.10 0.06 0.05 0.08 0.08 0,07 0,11 0.08 0,08

MgO CaO

6.84 9.91 6.74 9.99 6.45 10.12 2.13 4.95 3,18 4.62 2.69 7.29 2.01 3.71 1,72 4.52 1.95 6.78 7.59 9.73 8.46 9.96 4,97 9,68 5.55 7.29 5,81 8,10 2,54 6,01 1.98 7.36 1.17 1,75 0,92 1,51 2.81 2.66 2.90 1.60 2.77 3.36 3.47 1.25 2.88 1.18 2.98 1.52

Na,O K,O 2.57 0,72 2.57 0,64 2,36 0,51 3.91 1,16 3.24 1.76 2.69 0.68 3.71 1.70 2.99 2,01 4.03 0.30 2.81 0.47 2.47 0.32 3.56 0.47 3.28 0.66 2,96 0.61 4,59 1,16 4.48 1.14 2,51 1,33 2,05 2,56 2,79 3,32 1,73 2,92 2.46 2,08 1.76 4,24 1.62 2,63 1.70 2.78

F A K

0.39 -73 -38 0.45 -88 -39 0,36 -88 -33 0,13 -11 -51 0.14 -36 -60 0.15 -33 -37 0.10 -17 -38 0,09 -15 -33 0.09 -56 -62 0.35 -59 -40 0.36 -34 -27 0,24 -50 -53 0.26 -37 -43 0.29 - 7 -42 0.12 -18 -63 0.14 -39 -61 0,07 +17 -26 0,06 +30 - 6 0,14 +30 -17 0,16 +53 + 3 0,13 +42 -17 0,20 +93 +17 0,16 +94 + 2 0.14 +85 + 3

1 - tholeiites;2.3- andesites and dacites interlayered with basalts;4 - alumlnousbasalts:5 - andesiticbasalt swith higher alumin ium content;6-andesites with higheraluminium content;7 - subgreywackes interlayered with greywackesand pelites:8 - greyw ackes;9-pelltes,The numbers 1-9indicate the positionof the rock sin the total section.

24 Niko laiE.Kostov& AndreiA.Ivanov

A _

Fig.4.AFMdiagram for the metavolcanitesof the Lapland GranuliteBelt.Legend:1-tholeiites:2- aluminousbasalts:

3-andesiticbasalt:4- andesitesand dacites;5- bounda- rybetween tholeiiticand calc-alkalineseries (Irvine&Bara- gar 1971):6- bounda rylimits showingthe generaltrend ofevolution of themetavolcanites.

close to each other at various depths , and form ed in a period of increased tecton ic activi- ty (Bogdanova

Yefimov 1978). The presence of a tuffogenic cement in cong lomerates in the Kolvitsa tundra section (Predovsky 1987) also signifies volcanic activity.

o

GU·BULL.421.1991

In an AFM diagram (Fig. 4) the trend of chem ical compositional change of the metavol- canites from the Granulite Belt is located clo- se to the boundary between the field s of the tholeiitic and the calc-alkaline series. though closer to the latt er. On th e petro chemical dia- gram proposed by Piskunov (1987) for separa- ting the volcanites of oceanic and folded zo- nes. the average compos ition of all typical varieties of the gra nulite belt metavolcanites (see Table 2) is found within the field of the 'folded zone' , i.e. island arc plus continental margin. Of the various magmatic products of this zone the granulitic form ations. which were primarily volcano genic. fall within the field of island arc volcanic assoc iations (Fig. 5).

The diagrams of Lutz (1980) show that the basalts of the belt are close to both island arc associations and volcanites of oceanic origin (Fig. 6). Such an intermediate compos i- tion can probab ly be exp lained by their ocean- marg inal location in the proto- island arc sys- tem, which is characterised by AI-rich basalts (Ivanov

Kozlov 1987. Kozlov 1988b). The obta ined evidence is in good agreement w ith the data of Barbey et al. (1984) who sugges- ted the presence of two series, tholeiitic and calc-alkaline, in volcanic rocks of both the Tanaelv and the Granulite Belts.

The complete set of analytical data, show ing

20

10

OCEA IC VOLCA ITES

S

'FOLDED ZO E' OLCA ITE S

o o

o

o o

1S

CO TIE TAL ARGI

/ ~ o ,

I ARC

I \

\ 0 \

Q 0 001

" I

' 0/

~

7S B O

Si 0

+3Ca O%

Fig.5. (a) K-tand(b) 3TiO,+K,O-SiO,+3CaOdiagramsofPiskunov(1987) formetavolcanitesoftheLaplandGranuliteBell.

NGU- BULL. 421.1991 LaplandGranuliteBelt,KolaPeninsula,USSR 25

er

100 100

tOO

Ni 100 100

to

eo ~'1XX)

<>

10

v

?)O400 200400

=');~ " ~Yi

1000 10000 IQ 100 a! 10

=

IQOO . ₁₀₀₀ P [,₀₀₀₁

r '

1 '10(K C

L..w..~L-L....:....

er

Rb 100 Fig.6.Tholeiites(1)andalurni-

nous basalts(2) ofthe Granulite Belt plotted on diagrams by Lutz(1980).The romannume- rals indicate the fields and trendsof oceanic (I)andisland arc(11)basalts.

61 92

the init ial tholeiitic volcan ism , the occurrence of dacites in assoc iation with tholei ites in the very early stages , and the replacement of this bimodal association by At-rich volcanites which are close to calc-alkaline in composition , ac- cord with the patt ern of evolution of island arcs (Bogatikov

Tsvet kov 1988, using A.

Ringwood 's mater ials). The abse nce of alkaline volcanites in the section indicates the similari- ty of this assoc iation to that of juvenile arc complexes , which is con firmed by the presen- ce of abundant alumina-ri ch basalt w ith subor- dinate andes ite bas alts, andesites and dac ites .

Metavolcanites in the southwes t adjace nt to the Granulite Belt are represent ed by a wide range of rock -type s from thol eiites to dacites . In composition they can be comp ared to rneta- volcanites from the lower part of the sed imenta- ry-volcanic sequence. but at the same time

an almost comp lete abse nce of

units and the presence of metamagm atites w ith a low content of alkalies. The latter fact, taking into account the increasing alkalinity of vol- canites in island arc syste ms fro m the ocea n towards the contin ent, corre spon ds we ll w ith

the scheme of petrochemical zonat ion of the Lopian formations (Kozlov 1988b).

We should probably not look for a direct similiar ity between the pre-Loplan basement blocks and those of ocean ic or continental types ; nor should we accept the supposition concerning the similarity of the northwestern Kola reg ion complex to that of an island arc as entire ly correspond ing to the mode of forma- tion of Phanerozoic island arcs . If we assume that the granu lite complex was formed in an environment similar to that of an island arc, then we shou ld find comparable features with cor responding crustal types for the pre-Lopian formations . To define such features we have compared the rocks from the basement of the Lopian assumed island arc system with' those in adjacent blocks or microp lates. As a basis for tectonic zonation of the region we have

from the Institute of Precambrian Geology and Geoc hronology (Eart h's crust ... 1978).

In the present paper we have used some

data from the southwestern area. outside the

granu lite complex, together with published

material and information kindly pro vided by

26 NikolaiE.Kos to v&AndreiA.Ivanov NGU-BULL.421.199 1

Fig.7.AI,O,-f diagramsforEar- ly Arcnaean metavolcanites of the Kola Peninsu la and north- western Belomorie. legend: 1.

Allarechenskregion,2. Imandra region .3.Tersky block,4. ortn- western Belomorie and south- westernpart ofthe KolaPenin- sula.A- nolentes.B- ferrugi- nous basalts,C - anoesitic ba- salts.0 - dacites-rhyohtes.

06/}

f A

^f B

Q7~

'5 17 18 Al

z

07C

,~,

066 ^J'~

062

O X:

058 066

0:"> at2

o!

O~ 058 _·2

-

046 054

04

Q42 ^O~

0J8 ^Ql.6

JJ 14 /5 /6 17 18 AI ZOjlJ'.%

our colleagues V.V. Balagansky, V.1. Bolotov, M.M. Yefimov and V.1. Pozhilenko.

Vo lumes of typical rock-types in the north- eastern (Predovsky 1987) and southwestern areas peripheral to the granulite complex are, respectively; rhyolites - 6

and 4

dacites - 7 % and

%; andesites -

% and

%; andesitic basalts - 7 % and 7 %; basalts - 25 % and 42 % from 56 % and 75 %, the perce ntage of metavolcanites in the tota l volu- me of supracrusta l rocks . Differe nces betwee n the metamorph ic rocks of the southwestern and northeastern margina l areas are evident on compar ing them in AI,OJ - f diagrams (Fig.

7). A more detailed comparison of the most typical metavolcanites (except basalts, which are more widespread in the area to the sout h- west of the Granulite Belt) shows that within the groups o f similar mafic index they are characterised by a somewhat higher iron con- tent. The differences revealed in the compos i- tions of rocks form ing the pre-Lopian base- ment complexes in these northeastern and southwestern areas outside the Granulite Belt

are thus in agreement with our hypothesis for the probab le evolution of the Earth's crust in this region in pre-Lop ian time.

Rocks of a tentatively primary sedimentary origin within the belt constitute the bulk of the upper sequence and occur as interlayers in the lower, sed imentary-vo lcanogenic unit. With- in the upp er metasedimentary sequence, grey- wackes predominate and are confined to the lower part of the section. Pelites prevail in the upper part of the section. Approximate perce n- tages of the different rock-types in the section are as follows: greywackes 50% (group 8 in Table 2), subgreywackes 14% (group 7), arko - ses 1-2%, pelites 24% (9), tuffites 20% (only in Kolvtsa; Kozlov 1983).

Additional information on the primary charac-

ter of the rocks has been obtained from the

distribution of C

(Sidorenko & Sidorenko

1975, Petersilje et al. 1979). These data are

supp lemented by the results of a detailed stu-

dy of the most typical varieties of rocks shown

in Table 3 (58 determinations). The rock s inter-

preted herein as metasedimentary formations

NGU- BULL.421,1991 LaplandGranuliteBelt,KolaPeninsula,USSR 27

Table 3,Metamorphicrock softheGranulite Belt andsurroundingareasand their suggestedprimary character.

Metamorphic rock names

Schistoseanchimonomineralic tremolite amphibolites.

Garnet amphibolites, meso-melanocratic garnet-clinopyroxene plagioclase schlsts, meso-melanocraticgarnet-bipyroxene-plagioclase schists,mesocratic bipyroxene-plagioclase schlsts,

Garnet amphibolites, meso-melanocratic garnet-clinopyroxene plagiocla se schists, meso-melano cratic garnet-bipyro xeneplagioschi sts,mesocraticbipy- roxene-plagioclase schists,

Leucocraticgarnet-clinopyroxene-plag ioclase schists ,mesocratic bipyro xene- plagioclasescnlsts.meso-melanocratic garnet-amphi bolegneissesand gneiss- scnlsts.

Leucogratic and mesocratic biotite, amphibolebiotite, biotite amphiboleand amphibolegneisses and gneiss-schists,rare leucocra ticgarnet-orthopyroxene- plagioclaseschists.

Biotite and biotite-amphibolegneisses,gneiss-schists and granitegneisses.

Felsic granulites,garnet-biotitegneisses,garnet-biotite granitegneisses,gar- net-biotite plagiogranites.Pyroxene-garnet-biotiteplagioclase schists (?)Mica- ceous and amphibole-micaceous gneiss schists.

Felsic granulites. Garnet-micaceous, micaceous and amphibole micaceous qnelss-scrusts.

Felsicgranulites.

Felsic granulites, garnet-biotite, garnet-bimicaceous gneisses and gneiss- schists with kyanite, staurolite and sillimanite. Micaceous and amphibole- micaceous gneissschists.

Biotite-pyroxene gneisses

Muscovitequartzites

Primarynature ofthe rocks

Picrites

Tholeiitic basalts

Tholeiitic basalts

Andesitic oasaits

Andesitesand dacites

Rhyodacites andrhyolites

Greywackes

SUbgreywackes

Arkoses

Pelites

Tuffites ofintermediatecomposition

Quartzitic sandstones

Table4.Content of Corginvarious rocksgroupsfrom the Granulite Bell (in grit).

n x Variations

although somewhat scattered , they tend to fall in island arc fields (Fig.

Anothe r specific feature of the metaclastic rocks is the ir higher content of st ront ium (Koz- lov et al.

as compared with the typ ical strontium content for similar Phaner ozo ic and Precamb rian format ions . This can readily be exp lained by inherited features of the metavol- can ites , while simultaneous volcan ic activ ity and its inftuence on sedimentation test ifies to the act ive tecton ic regime.

Data byTAFedkova(Petersilje et al. 1979)

have a less homogeneous C

content than the metavolcanites and, in genera l, are en- riched in th is element. The C

content in the pelites , for example , reaches 2.4

according to the data of TA Fedkova (Petersilje et al.

1979),

To estimate the quantitative characte ristics of weathe ring and sedimentation we calcu lated the intensity

and extensiveness

of w eatherin g and the degree of sed imenta ry differentiation (d) (Predovsky

Th ese parameter s (Table 5) allow us to refer the metasedimentary form ation s of the Granulite Belt to the zones of stro ng or maximum-act ivi- sed downwar ping. This is in goo d agr eement with the conc lusion regarding the active tecto- nic regime during the time of form ation of the metavolcanogenic sequences. This conc lus ion is supported by plots of metamorphosed clas- tic rock samples in Bhat ia's

diagrams ;

Andesitesand dacites Quartzitesandarkoses SUbgreywacke s Greywackes Clastolith s Pelites

10 8 10 29 47 9

100 175 110 140 140 300

40-200 30-500 40-200 40-600 30-600 50-1400

28 Niko leiE.Kostov&AndreiA.Ivanov _{GU -BULL.421,1991}

' 2

1 2

.

o

L

'\7]

0 4

'" .

"

.

. ..

a

o

. . .

I

4

1 2

_-

'St.:;. %

.. I .

~ ·/ _. I

•

" I

4

t o

. .

05 . .

/

; '

0 0

/.;

-

4 ,K.ZO/N'JZO.

%

0

"--,

2

N . .. _.

Fig.9.Diagrammatic SW-NEprofiles showing the suggested geodynamicevolution ofthe LaplandGranuliteBelt (not drawn to scale).Legend:1 -tholeiites;2-andesite-dacites;3- aluminousandesiticbasali s andbasalts:4-sedimentar y rocks;5 -intrusive complex;6- sedimentation;7 - dominantcrustalmotions.11and I indicate theareas of theGranuliteBelland its southwestern Lopianperiphery,respectively.

Based on a comparative increase in the general intensity and character of the paleotec - tonic regime, the Lopian format ions of centra l and northwestern Kola can be separated into three regions: (1) Granulite Belt; (2) Allarechka region; (3) Kolmozero-Voronya (Predovsky 1987). This const itutes a kind of tectonic zona- tion similar to that report ed earlier for alurni- nous basalts (Kozlov 1988b). This zonation can be traced when comp aring the approx ima- te volumes of metavolcanic and metasedimen- tary rock s of the above com plexes (Table 6).

A more local zonation is identifi ed by compa- ring metasedimentary format ions from the central and south-southwestern parts of the Granulite Belt. In general, the rock s are simi- lar in major element contents , but diff er consi- derably in a number of minor elements. This is clearly seen in the metapelites, which in the south-southwest are noticeably enriched in

coppe r, nickel, cobalt, chromium and boron (Table 7), testify ing to the considerable effect on their format ion of simultaneous volcanism.

The above differe nce becomes clear on exami- ning the complete set of data. Thus, AI-rich metabasalts, which form considerable volumes in the upper part of the section of the vol- canogenic formations in the centre of the belt, are absent beneath the metasedimentary sequ- ences of the southwestern part of the belt.

This indicates that, here, sedimentation began earlier, while within the central parts of the belt the intensive simultaneous volcanic pro- cesses cont inued.

Discussion

The complete geological and petrochemical

data allow us to trace the sequence of proces-

ses involved in the formation of the Lapland

Granulite Belt (Fig. 9).

NGU-BULL. 421.1991

Probably in Lopian time, dur ing a phase of compressio n of the Earth's crust, the Belomori- an megablock underthrusted the Kola mega- block forma tions along the Belomorian deep fault. Defo rmations and metamo rphism dated to 2.87 - 2.66 Ga in the Lopian basement (Pet- rov et al. 1986) probably reflect this stage of compress ion, though this age might be some- what younger. Differences in composition of the rocks of the pre-Lopian basement blocks led to the initiation of subduct ion which defi- ned the characte r of the volcanic activity. At the initial stage , under conditions of higher tecto nic activity which contro lled the uprise of magmatic sources at various depths , effusi- on of tholeiitic and andesite-dacite lavas occur- red accompa nied by outbursts of dacitic and andesitic tuffs . Volcanite sequences were for- med, evidently in a submarine environment.

This is suppo rted by the presence of conglome- rates with a tuttaceo us cement, partially wea- thered and containingadmixtures of sedimenta- ry material in the lower section. During a subse- quent volcanic cycle the lava compos ition chan- ged due to an increase in the aluminium con- tent , and as a result thick units of aluminous basalt were accumulated; in the final stage they were rep laced by andesitic basalts and andesites with even higher contents of AI,O,.

With downwarping of the Lopian basin and disp lacement of the boundary of volcanism to the northeas t of the underthrust ing plate (Fig.

9), simultaneously with volcanic activity in the outer part of the belt, the sedimentation conti- nued at the same time as volcanism decrea- sed both within and to the southwest of the belt. The sedimentation resulted in the forma- tion of clasto lithic sequences , gre ywackes , sUbgreywac kes and, after the complete cessa- tion of volcanic activity, of pelites.

After the format ion of the volcano-se dimen- tary Lopian complex had been complet ed, the next stage of tectono -magmatic activ ation

LaplandGranulite Belt,KolaPeninsula,USSR 29

Table 5.Quantitative characteristicsof the degree of weath- ering of the parent rocks andof the degree of differentia- tion for sedimentsfrom the GranuliteBell.

Region s

w,

Kolvitsa 39 1.1 1.0 10.3

Northwestern part 39 1.3 1.1 8.7

oftheBelt(USSR)

Inari 42 1.2 1.6 12.2

Belt(total) 39 1.3 1.2 17.2

Note:Calculations were madein molecularpercentages.

W, (intensity01weathering)=Aav +Kav.whereAavandKavare averageAand Kvalues lorpsammiteandpetite:

W, (extensiveness ofweathering)iscalculated asa ratioof the maximumrange01pointsforthe sedimentary rocks(their basi- city. parameterF)tothe Faxisdivisionvaluein theFAKdia- gram(Predovsky 1970):

dav (degreeof sedimentarydifferentiation)=A

Fflorpelites 1000 orpsarnrmtes. where AandFare meanvalues:

dmax (degree01maximum Alorpelitemax sedimentarydifferentiation) F forpsammitemin.1000 A= AI,O,- (CaD'+Na,O+K,O).whereCaD'=CaD-CO,:

K= K,O-Na,O:

F= 5iO,

Fe,O,+FeD+ MgO

Table 6.Appro ximate volumeproportionsof the most typi- cal rock groups of the Granulite Belt (1), AlJorechensk(2) and Kolmozero-Voroninskregions of KolaPeninsul a.

Rock grou ps Regions

1 2' 3'

Vo/canites 50 56 75

Rhyodacites 4 4 10

Andesitesandandesiticbasalis 8 6 3

Tholeiites 22 24 35

Aluminous basalts 16 10 5

Ferruginous basalts 3 2

Komatiit icbasalis.picrites and 9 20 hyperbas ites

Sedimentaryrocks 50 44 25

Greywackes 25 20 17

SUbgreywackes 7 7 3

Arkoses 1 1 2

Pelites 12 2 1

Tuffites 5

Quart zite s,sulphide- carbon aceous 14 2 rocks,conglomerate andpyritic

rocks

, - According to the data from Predovs ky (1987).

Table7. Comp os itionof pelites from thecentral(IA-66 -IA-73) and south-sout hwesternparts(2622-2446) ofthe GranuliteBell.

Sampleno SiO, TiO, AI,O, Fe,O, FeO MnO MgO CaO Na,O K,O Cu Ni Co Cr B

IA-66 66.29 0.98 14.96 0.11 9.63 0.08 2.61 1.03 1.34 2.28 49 34 19 140 2

IA-65 69.49 0.40 15.39 1.15 5.78 0.06 2.30 1.21 1.47 2.57 36 17 10 130 2

IA- 118 58.75 0.79 19.96 6.90 3.96 0.09 3.20 0.96 1.19 2.87 30 53 19 130 3

IA-73 62.26 0.97 16.65 0.00 11.15 0.10 2.94 1.00 0.58 1.66 62 83 20 140 13

x

2622 62.09 0.69 17.21 0.47 8.13 0.15 4.19 1.33 1.54 1.75 130 330 47 830 16

2470 59.20 0.84 18.87 3.50 6.10 0.10 2.00 1.88 2.04 1.98 120 130 29 700 8

2476 64.61 0.68 16.76 2.50 5.79 0.10 2.06 1.24 1.24 2.09 55 100 24 700 8

2720 58.06 0.98 18.63 1.67 8.31 0.14 5.11 1.77 1.32 1.23 160 370 51 470 49

2446 60.86 0.69 18.10 4.70 3.06 0.05 2.39 0.48 1.72 4.35 10 90 20 380 31

x

30 Niko laiE.Koslov& AndreiA.Ivano v ^{GU·BULL.421,1991}

- ^, ----

P aL ea oas ' n

geL o, or ' a

meo ab ock '"

oc~

2 Jroli t.

Fig.8.RatiodiagramsofTiO,.AI,O,/SiO,.K,DI a,Dand AI,O /(CaO· a,O)toFe,O,+FeO,MgO(Bhatia1983).Thelined areas show thefields correspondingto:I. oceanic islandarcs:11 - continental island arc:III• activecontinental margin:IV• passivecontinentalmargin.Legend:1•greyw ack es:2• subgreywackes;3-arkoses ofgranulitebelts;4.averagevalues for groups '·3(encircled symbols correspon dingto these gro ups);5 -averagevaluefor metaclastitesof theentire belt.

began at 2.5 - 2.3 Ga (or maybe earlier) with intrusions of komatiitic, gabbro-Iabradorite and iron-rich mafic compos ition (Ko zlov 1986, Suk- hanov et a1.1987, Kozlov et al. 1988b).

The model presented here describes only a part of the proto-arc syste m composing the granu lite comp lex. Elaborat ion of the detailed development of the crust in this exte nsive region requires additional studies in other terri- tor ies, which fall outside the scope of the pre- sent paper. For such work it will be necess- ary to take into account the described zonal structure of the Lopian formations.

The model does not show the furt her evolu- tion of the complex. One can assume that

Belomor ian megablock relative to the Kola block along the Lapland deep suture zone resulted in an eventual burial of the complex down to depth s where the combination of pressure and temperature conditions facilitated metamorph ic transformations in granulitic taci- es and part ial palingenesis of supracrustal rock s. In subsequent stages the complex was

uplifted, exposed and eroded . Presumably such stages of developm ent were repeated.

Based on the interpretation of the primary origin of the rocks .and the geodynamic deve- lopment of the belt, the propos ed model (see also Kozlov 1984) is most similar to that of Horrnann et al. (1980). It is also similar to the interpretation simultaneously and independent- ly proposed by other scientists studying the Lapland Granulite Belt (e.g. Barbey et al.

1984), although it differ s greatly from the lat- ter in terms of structure and age correlation and therefore in relationships with ot her struc- tures of the region.

Ackno wledgements

The auth o rs express the ir sinceregra titude to the scienu- ficsupe rvisorofthe project under whichthe prese ntwork has been done.AA Predo vsky;also to colleagues E.V.

Martyn ovand L.1. erovich whohelped alotinprocessing the data; and colleagues V.A. Melezhik. M.1. Dubrovsky.

V.P.Petrov,A. .Vinogradov.Zh.A.Fedotov,V.1.Bolotov, A.A.Zhangurov. .V.Sharovand V. .Glaznevfor valua- blediscu ssionsandassistancein ourwork.Wewouldalso like to thank M.Often and another anonymous reviewer fortheircriticalcommentsonearlier versionsofthe manu- script; and D. Robens for correcting the English in the finalversion.

NGU-BULL.421,1991

Re ferences

Balagansky,V.V.,Bogdanova,M.N,& Kozlova,N.E.1986:

Structural-metamorphicevolutionof thenortheastBelo- moriye. Acad. Sci. USSR. Kola Branch.Apatity. 100 pp.(inRussian).

Barbe y,P..Convert,J..Martin,H..Moreau ,B.,Capdevila, R.& Hameurt,J.1980:Relationsh ipsbetweengranite- gneiss terr ains.greenstone belts andgranulitebelts in the Archean crust of Lapland (Fennoscandia). Geol.

Rundschau69,648-658.

Barbey,P.,Convert,J.,Moreau,B.,Capdevila.R.&Hame- urt, J. 1984: Petrogenesis and evolution of an Early Proterzoic couis lona lorogenic belt: the granulite belt of Lap land and Belomorides (FennosCandia).Bull. Ge- 01.Soc.Finland 56.161-1 88.

Barbey, P.,Bernard-Griffiths,J.

s

Belyaev,K.D.1971:New dataon the structure,geology&

metallogenyof granul iteformationof theKola Peninsu- la. In Problems of magmatism in the Baltic Shield.

Nauka,Leningrad ,218-225 (inRussian).

Bernard,Griff iths,J..Peuca t,J.J..Pstaire, B.,Vida l, Ph.,

-Convert, J, & Moreau, B. 1984: Isotopic data (UPb,

RbSr,PbPb and SmNd)of maficgranulites from Fin- nishLapland.Precamb.Res.23.325-348 .

Bhatia,M,R.1983:Platetectonic andgeoc hemicalcomposi- tion of sandstone.J.Geol.Geoch. 91.611-627. Bogatikov,O.A.&Tsvetkov,AA 1988:Magmaticevolution

ofisland arcs.Nauka,Moscow.248pp.

Bogdanova,M.N. & Yefimov , M.M.1978:Mainstag es of tectonicevolutionand metamorphism in the Kandalaks- na-Kotvit sagranulitezone.In Tectonicsand deep struc- tures oftheBalticShieldeasternpart.Acad.Sci.USSR.

KolaBranch.Apatity.28-36.(in Russian).

Bogda nova.M.M.&Yefimov,M.M .1984:Geologicalstructu- res of the Kandalaksha-Ko lvitsa structure-formation zone. InPrecambriangeology of the Kola Peninsula.

Acad.Sci.USSR.KolaBranch,Apatity.19-27(in Russi- an).

Eart h'scrust intheeasternpart of the BalticShield.1978:

28-36.(inRussian).

Eskola,P.1952:On the granulitesof Lapland.Amer.J.Sci.

I,133-17l.

Hor mann,P.K.,Raith,M.•Rass,P.,Ackarmand,D.& Sei- fert,F. 1980:The granu lite comp lex of Finnish Lap- land: petrologyand metamorphicconditions in the lval- [oti-tnarqarviarea.Bull.Geot.Surv .Finl.308.98pp.

Irvine,T.N.& Baragar,W.R.1971:A guide to chemicalclas- sificationof the common volcanicrocks.Can.J.Eart h Sci.8.523-548.

Ivanov,AA& Kozlov,N.E.1987:Arcneanhighlyalurnlnite- rous rnetabasalts of the KolaPeninsula.In Magm atism.

metamorphism and geochronology of the Precambrian in the East European Platform related to large-scale mapping.Acad.Sci.USSR.Karelian Branch.Petroza- vodsk,79(inRussian).

Kozlov.N.E.1983:Anew version of stratigraphic interpreta- tion for the Kolvitsa zonesection of thegranu litebelt . InSedimentation basins and volcan ism zones of the Precambrianin the Kolaregion .Acad.Sci.USSR.Kola Branch,Apatity,69-81 (inRussian).

Kozlov, N.E. 1984: On reconstruction of tectonic regime ofthet.aplandgranulitebeltformation.In Geology and formation history of the Kola Peninsula Precambrian structures. Acad. Sci. USSR, Kola Branch, Apatity, 78-81(inRussian).

LaplandGranuliteBelt,KolaPeninsula.USSR 31

Koz lov, N.E. 1986: Ore-bea ring properties of garnet- amphibole-pyroxe ne cry stalline schists inthe Western Porya Bay (The Kolvitsazone of granulitebelt).InPro- ceedings of V Confere nce of young scientists, geol.

section,geochem istry,mineralresources.VINIT!.Oep.

No.7294-B-86.37-48 (inRussian).

xono v,N.E. 1988a: Fragmentation andcorr elation of the Laplandgranulitebelt.Lithologyandmineral resources.

N5.11-117 (inRuss ian).

Kozlov,N.E.1988b:On some features of petrogeochemi- catzonalityof the KolaPeninsulaaluminiferous Upper- Arcnean greenstone belts.Acad.Sci.USSR.Karelian Branch.Petroze voask ,156-164(in Russian).

Kozlov,N.E.,Ivanov, A.A. & Nerovich , L.1.1988a: Salna tundr a zone of the Laplandgranulitebelt.OokladyAN SSR,298.1442-1445 (in Russian).

Kozlov,N.E., Ivanov,AA & Nerovicn, L.1. 1989:Ba and Sr distr ibut ion in Archean metamorphic rocks in the south and south-westof the KolaPeninsula.Geocnemis- try.N 7,1058-1061(in Russian).

Kozlov,N.E..Ivanov,AA &Nerovich ,L,I.1990a:Granuli- tesof the Baltic Shield - proto-islandarcformationof theEarlyPrecam brian stageof the Earth'scrust evoluti- on (preprint),16 pp.(in English ).

Koztov,N.E.,Ivan ov,AA&Nero vich,L.I. 1990b:The Lap- land granulitebelt- primaryorigin andevo lutio n.Acad.

Sci.USSR.Kola Centre. Apa tity.170 pp.(synopsis in Eng lish).

Ko zlov,N.E.,lvanov,AA &Predovsky.AA 1988b:Compo- sition and series of the Ni-bear ing metamaf ites ofthe Lovno region (the KolaPeninsula).OokladyAN SSSR, 302.N 2.394-396 (in Russian).

Kozlo v, N.E.Lipov,A.P.,Nazarenko,V.O.,Nerovich,L.I.&

Sargsian, G.O. 1990c: Prima ry features of the Kola granulite beltenderbites . Geocnemistry,N 4,591-498 (synopsisinEng lish ).

Kry lova,M.D.1983:Geologic-geochemicalevolution of the Lapland granulitecomplex.Nauka.Leningrad,160 pp. (in Russian).

Lutz,B.G.1980:Geochemistry of oceanic andcontinenta l magmatism.Nauka.Moscow.247 pp.(in Russian).

Marker, M. 1985: Early Protero zoic (c. 2000 - 1900 Ma) crustaItectonicdivision and tectonogenesis.Nor.geol.

unders.Bull..403.55-74.

Merilainen, K. 1976:The granulite complex and adjacent rocks in Lapland, northern Finland. Bull. Geol. Surv.

Finland,281.199 pp.

Mikkola,E.194 1:The generalgeolog icalmap of Finland, Sheets B7, C7, 07, Muonio, Sodankyla, Tuntsajok i.

Explanationtothe mapand rocks.Suomen geol.Toimi- kunta.Helsink i.24.283-295.

Petersilje,I.A.,Fedkova,TA&Pavlo va,MA,1979:Gases and organicmatter in the rocks of the Archean granuli- te complexof theKolaPeninsu la.Geochemis try,N 12.

1883-1 888(in Russian ).

Petro v,V.P.,Belyaev ,O.A.•voios nina. Z.M., Bogdanova.

M.N.& Ivliev,A.1. 1986:Metamorphism of supracrustal comp lexes of the Early Precambri an (north-eastern part of the Baltic Shield). Nauka, Leningrad. 272 pp.

(inRussian).

Piskunov,B.1.1987:Geolog ical- petrolog icalfeatures ofislan- dare volcanisrn.Nauka.Moscow.237 pp.(inRussian).

Predovsky,AA 1970:Geochemicalreconstruct ionof prima - ry composition of Precambrian metamorphozed voi- canog enou s-sedim entaryform ations.Acad.Sci.USSR.

KolaBranch,115 pp.(in Russian).

32 Nikola iE.Kostov& AndreiA.Ivanov

Predovsky, AA (ed, 1987): Preca mbrian volcanism and sedimentologyintheBalticShield.Nsutcs,Leningrad. 185pp.(inRussian).

Raith ,M.& Raase,P.1986,High-grade metamor phismin the granulite belt01FinnishLapland.InDawson,J.B., Carswell, D.A., Hall, J. &Wedepohl. H.H. (eds.).The natureof thelower continentalcrust. Geol.Soc. Lon- don,Spec.Publ. 24,283-295.

Rund kvist,D.V.&Mitrolanov,F.P. (eds.1988):Precambrian Geology of the USSR.Nauka,Leningr ad,440 pp. (in Russian).

Sidorenko ,SA & Sidorenk o,AV.1975:Organicmatter in Precambr ian sedimentary metarnorp nic rocks. Nauka, Mosco w.138pp.(InRussian).

GU- BULL.~2 1.1991

Sukhanov,M.K.,Terekhov,E. .,Levitsky, V.1. 1987: ew dataon structure andradiological age 01 the t.aptand granulite beltformation (the Kandalaksha coast 01 the WhiteSea).DokladyAn SSSR,295,N6.1437-1440(in Russian).

Vinogradov,L.A.,Bogd anova,M.N.&Yelimo v,M.-I.1980:

Granulitebeltof the KolaPeninsula.Neak«,Leningrad, 208pp. (inRussian).

Zykov,S.I., Stupnikova, N.I., Sidorenko.S.A. 1984: Pb isotopes01 theGranuliteBelt rocks ofthe KolaPeninsu- la.Ves tnikMGU,ser.4,geology.N3,58-64(inRussian).

Manuscript received June 1990;revised typescript January 199 1; accepte d April 1991.